Fluoropolymers containing vinylidene fluoride units (e.g., copolymers of vinylidene fluoride and ethylenically unsaturated monomers such as hexafluoropropane) have particular utility in high temperature applications, including seals, gaskets, and linings, as described, for example, in Brullo, R. A., "Fluoroelastomer Rubber for Automotive Applications," Automotive Elastomer & Design, June 1985, "Fluoroelastomer Seal Up Automotive Future," Materials Engineering, October 1988, and "Fluorocarbon Elastomers," Encyclopedia of Polymer Science and Engineering, vol. 7, pp. 257 et seq. (2d ed., John Wiley & Sons, 1987). One reason is that such fluoropolymers, when cured, have good resistance to damage by heat, solvents, corrosive chemicals, and steam. However, the curing process is generally very slow, necessitating the use of a cure accelerator. A variety of organo-onium compounds have been proposed for this purpose.
In addition, during the manufacturing process (particularly where injection molding is used) the cured polymers generally adhere to the surface of the mold. As a result, a shaped article prepared from the fluoropolymer is frequently torn or damaged when removed from the mold. Also, the incorporation of a mold release agent into the polymer can have serious adverse effects on the physical properties of the cured composition (e.g., Mooney Scorch, shrinkage, and compression set) which can limit the successful commercial use of the cured composition. Deposits of polymer on the mold cavity surface ("mold fouling") and poor release of the shaped, cured article from the mold are major reasons for defects, resulting in rejection of the article (which then adds to the expense of manufacturing such articles).
One possible solution to the mold release problem is proposed in Kolb et al., U.S. Pat. No. 5,262,490 (which is hereby incorporated by reference). Kolb describes compositions containing a phosphonium or ammonium salt, a sulfonium compound, and (optionally) a polyhydroxy compound that are designed to perform the dual functions of accelerating fluoropolymer cure and providing mold release properties.